ICCB Species distribution modelling and validation

Abstract

In this script we are fitting species distribution models to the data of koalas (Phascolarctos cinereus) in the South-East Queensland (SEQ) region under current environmental conditions, which we will predict into future environmental conditions.

We wrote this script drawing on some of the following resources:

-Ecocommons Notebooks https://www.ecocommons.org.au/notebooks/

-Damaris Zurell’s SDM Intro https://damariszurell.github.io/SDM-Intro/

https://damariszurell.github.io/EEC-MGC/b4_SDM_eval.html

Import packages

library(dplyr)

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

library(purrr)
library(ggplot2)
library(terra)

terra 1.7.78

library(sf)

Linking to GEOS 3.12.1, GDAL 3.8.4, PROJ 9.3.1; sf_use_s2() is TRUE

library(predicts)

Warning: package 'predicts' was built under R version 4.4.3

library(blockCV)

Warning: package 'blockCV' was built under R version 4.4.3

blockCV 3.1.5

library(ecospat)
library(usdm)
library(randomForest)

Warning: package 'randomForest' was built under R version 4.4.3

randomForest 4.7-1.2

Type rfNews() to see new features/changes/bug fixes.

Attaching package: 'randomForest'

The following object is masked from 'package:ggplot2':

    margin

The following object is masked from 'package:dplyr':

    combine

library(precrec)

Warning: package 'precrec' was built under R version 4.4.3

library(corrplot)

corrplot 0.92 loaded

# Install the mecofun package, used in the materials at https://damariszurell.github.io/SDM-Intro/
library(devtools)

Loading required package: usethis

devtools::install_git("https://gitup.uni-potsdam.de/macroecology/mecofun.git")

Skipping install of 'mecofun' from a xgit remote, the SHA1 (feb82c4a) has not changed since last install.
  Use `force = TRUE` to force installation

# Load the mecofun package
library(mecofun)

Load koala presences and background points

They are loaded as spatvectors, but we also want them as dataframes for model input requirements.

koala_occ <- vect("Data/Biological_records/SEQ_koala_occurrences.shp")
background <- vect("Data/Biological_records/background_points_2.5k_random.shp")

# Make a dataframe of just x, y and presence
koala_occ_df <- koala_occ %>% 
  as.data.frame(geom = "XY") %>% 
  dplyr::select(x,y) %>% 
  mutate(Presence = 1)

head(koala_occ_df)

background_df <- background %>% 
  as.data.frame(geom = "XY") %>% 
  dplyr::select(x,y) %>% 
  mutate(Presence = 0)

head(background_df)

# Combine to one
pr_bg <- rbind(koala_occ_df, background_df)

Load environmental covariates

Loading current covariate rasters. We formatted these rasters in the same way as the Koala data, so that they are all in the same projection and extent. We did this in the script: ‘ICCB_Environmental_data.qmd’

covs_current <- rast("Data/Environmental_variables/current_bioclim.tif")


# Define the BIOCLIM names for the raster layers
layer_names <- c(
  "BIO1_Annual_Mean_Temp",
  "BIO2_Mean_Diurnal_Temp_Range",
  "BIO3_Isothermality",
  "BIO4_Temperature_Seasonality",
  "BIO5_Max_Temp_Warmest_Month",
  "BIO6_Min_Temp_Coldest_Month",
  "BIO7_Temperature_Annual_Range",
  "BIO8_Mean_Temp_Wettest_Quarter",
  "BIO9_Mean_Temp_Driest_Quarter",
  "BIO10_Mean_Temp_Warmest_Quarter",
  "BIO11_Mean_Temp_Coldest_Quarter",
  "BIO12_Annual_Precipitation",
  "BIO13_Precip_Wettest_Month",
  "BIO14_Precip_Driest_Month",
  "BIO15_Precip_Seasonality",
  "BIO16_Precip_Wettest_Quarter",
  "BIO17_Precip_Driest_Quarter",
  "BIO18_Precip_Warmest_Quarter",
  "BIO19_Precip_Coldest_Quarter")

names(covs_current) <- layer_names

Covariate selection

Option 1. Narrow down potential covariates based on ecological knowledge

For this example, we had advice from CSIRO scientists who conducted an expert elicitation to gather a set of potential covariates that are likely to be important for koalas. We use this knowledge to filter out the key bioclim variables.

We select the following: Bio5 : Max temp of the warmest month (mainly for the northern populations) Bio6 : Min temp of the coldest month (mainly for southern populations, which essentially excludes alpine regions) Bio12 : Annual Precipitation Bio15 : Precipitation seasonality (coefficient of variation)

for(i in 1:nlyr(covs_current)) {
  terra::plot(covs_current[[i]], main = names(covs_current)[[i]])
}

Show the four from expert elicitation the layers

covs_current_expert <- subset(covs_current, names(covs_current) %in% c("BIO5_Max_Temp_Warmest_Month", 
                                                                       "BIO6_Min_Temp_Coldest_Month", 
                                                                       "BIO12_Annual_Precipitation", 
                                                                       "BIO15_Precip_Seasonality"))

for(i in 1:nlyr(covs_current_expert)) {
  terra::plot(covs_current_expert[[i]], main = names(covs_current_expert)[[i]])
}

Extract environmental covariate values from presence and background locations (training locations)

train_PB_covs <- terra::extract(covs_current, pr_bg[,c("x", "y")], xy = T)
train_PB_covs <- cbind(train_PB_covs, pr_bg["Presence"])

# Remove rows where there's values missing from at least one covariate
print(paste0("RECORDS FROM ", nrow(train_PB_covs) - sum(complete.cases(train_PB_covs)), " ROWS IN TRAINING DATA REMOVED DUE TO MISSING COVARIATE VALUES"))

[1] "RECORDS FROM 68 ROWS IN TRAINING DATA REMOVED DUE TO MISSING COVARIATE VALUES"

train_PB_covs <- train_PB_covs[complete.cases(train_PB_covs), ] 
train_PB_covs <- dplyr::select(train_PB_covs, -ID)

head(train_PB_covs)

Thin the koala presence points (for tutorial only)

We now thin the presences to reduce the number of points to a manageable size for plotting and modelling. This is not a recommended step for real data, but is done here to make the tutorial run faster and to make the plots clearer.

train_PB_covs_pres <- train_PB_covs %>% filter(Presence == 1)
train_PB_covs_bg <- train_PB_covs %>% filter(Presence == 0)

# Thin the presences for plotting
train_PB_covs_pres_thin <- train_PB_covs_pres[sample(nrow(train_PB_covs_pres), 10000), ]

# Combine back into both presence and background
train_PB_covs_thinned <- rbind(train_PB_covs_pres_thin, train_PB_covs_bg)

Check correlation and multicollinearity of covariates

Correlation plot

There are several different methods for creating correlation plots.

ecospat.cor.plot(covs_current_expert)

Using the corplots package

For a simple and quick plot.

corplots <- ENMTools::raster.cor.plot(covs_current_expert)
corplots$cor.mds.plot

corplots$cor.heatmap

Here, we use the corrplot package to create a correlation plot of the selected covariates (this is taken from an EcoCommons Australia notebook).

# Select columns by their names
cor_data <- train_PB_covs[, names(train_PB_covs) %in% c("BIO5_Max_Temp_Warmest_Month", 
                                                        "BIO6_Min_Temp_Coldest_Month", 
                                                        "BIO12_Annual_Precipitation", 
                                                        "BIO15_Precip_Seasonality")]

# Check the structure of the numeric data
str(cor_data)

'data.frame':   87611 obs. of  4 variables:
 $ BIO5_Max_Temp_Warmest_Month: num  29.7 30.5 30.5 29.7 30.2 ...
 $ BIO6_Min_Temp_Coldest_Month: num  9.39 8.94 8.49 9.96 8.96 ...
 $ BIO12_Annual_Precipitation : num  1238 1165 1161 1223 1109 ...
 $ BIO15_Precip_Seasonality   : num  92.9 98.8 99.5 88.9 97.2 ...

# Calculate the correlation matrix for the numeric columns
cor_matrix <- cor(cor_data, use = "complete.obs", method = "pearson")


corrplot(cor_matrix,
         method = "color",            # Use colored squares for correlation
         type = "upper",              # Show upper triangle only
         order = "hclust",            # Reorder variables hierarchically
         addCoef.col = "black",       # Show correlation coefficients in black
         number.cex = 0.5,            # Reduce the size of correlation labels
         tl.col = "black",            # Text label color
         tl.srt = 30,                 # Rotate labels slightly for readability
         tl.cex = 0.5,                # Reduce text size of variable labels (set smaller valu)
         cl.cex = 0.8,                # Reduce text size of color legend
         diag = FALSE,                # Hide diagonal
         col = colorRampPalette(c("#11aa96", "#61c6fa", "#f6aa70"))(200),
         sig.level = 0.01, insig = "blank")

Variance Inflation Factor (VIF)

If you find corrplot is hard for you to make decisions, we can use Variance Inflation Factor (VIF). VIF is another statistical measure used to detect multicollinearity in a set of explanatory (independent) variables in a regression model.

Interpretation:

• VIF = 1: No correlation
• VIF > 1 and <= 5: Moderate correlation; may not require corrective action.
• VIF > 5: Indicates high correlation. Multicollinearity may be problematic, and further investigation is recommended.
• VIF > 10: Strong multicollinearity. The variable is highly collinear with others, and steps should be taken to address this.

# usdm::vif(covs_current_expert) # just VIF for all covariates
usdm::vifstep(covs_current_expert) # Variance Inflation Factor and test for multicollinearity

No variable from the 4 input variables has collinearity problem. 

The linear correlation coefficients ranges between: 
min correlation ( BIO15_Precip_Seasonality ~ BIO6_Min_Temp_Coldest_Month ):  -0.2756697 
max correlation ( BIO12_Annual_Precipitation ~ BIO6_Min_Temp_Coldest_Month ):  0.8769718 

---------- VIFs of the remained variables -------- 
                    Variables      VIF
1 BIO5_Max_Temp_Warmest_Month 2.751370
2 BIO6_Min_Temp_Coldest_Month 4.528719
3  BIO12_Annual_Precipitation 6.888077
4    BIO15_Precip_Seasonality 1.263385

Exploration of the koala presence and background data

It is good practice to assess where in the environmental space the presence and background points are located. This can help to identify if there are any potential issues with the data, such as a lack of background points in certain areas of environmental space, and should show any patterns in the data that the model should pick up.

# Iterate over all of the variables to create density plots of the background and presence data
for(i in 1:ncol(train_PB_covs_thinned)) {
  
  print(ggplot() +
          geom_density(data = train_PB_covs_thinned, 
                       aes(x = .data[[names(train_PB_covs_thinned)[i]]], fill = as.factor(Presence)), 
                       alpha = 0.5) +
    theme_bw() +
    labs(title = names(train_PB_covs_thinned)[i]))
  
}

First Model: GLM model fitting

# Make a folder to save outputs
dir.create("Outputs/GLM_outputs", showWarnings = F)

Null model

Null model: no explanatory variables or predictors are included.

It is always helpful to create a null model as a benchmark to assess how the inclusion of explanatory variables improves the model.

# Fit a null model with only the intercept
null_model <- glm(Presence ~ 1,
                  data = train_PB_covs,
                  family = binomial(link = "logit"))

# Check the model results
summary(null_model)

Call:
glm(formula = Presence ~ 1, family = binomial(link = "logit"), 
    data = train_PB_covs)

Coefficients:
            Estimate Std. Error z value Pr(>|z|)    
(Intercept)  4.07488    0.02636   154.6   <2e-16 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

(Dispersion parameter for binomial family taken to be 1)

    Null deviance: 14884  on 87610  degrees of freedom
Residual deviance: 14884  on 87610  degrees of freedom
AIC: 14886

Number of Fisher Scoring iterations: 7

GLM Model 1 - expert variables

glm_model_1 <- glm(Presence ~ 
                     BIO5_Max_Temp_Warmest_Month + 
                     BIO6_Min_Temp_Coldest_Month + 
                     BIO12_Annual_Precipitation + 
                     BIO15_Precip_Seasonality,
                   data=train_PB_covs_thinned,
                   family = binomial(link = "logit"))

# Check the model results
summary(glm_model_1)

Call:
glm(formula = Presence ~ BIO5_Max_Temp_Warmest_Month + BIO6_Min_Temp_Coldest_Month + 
    BIO12_Annual_Precipitation + BIO15_Precip_Seasonality, family = binomial(link = "logit"), 
    data = train_PB_covs_thinned)

Coefficients:
                              Estimate Std. Error z value Pr(>|z|)    
(Intercept)                 -6.4382514  1.5863788  -4.058 4.94e-05 ***
BIO5_Max_Temp_Warmest_Month -0.6066972  0.0524073 -11.577  < 2e-16 ***
BIO6_Min_Temp_Coldest_Month  0.8786225  0.0283030  31.043  < 2e-16 ***
BIO12_Annual_Precipitation  -0.0029178  0.0002755 -10.592  < 2e-16 ***
BIO15_Precip_Seasonality     0.2481506  0.0108872  22.793  < 2e-16 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

(Dispersion parameter for binomial family taken to be 1)

    Null deviance: 8758.5  on 11463  degrees of freedom
Residual deviance: 5702.2  on 11459  degrees of freedom
AIC: 5712.2

Number of Fisher Scoring iterations: 6

# These response curves don't look very helpful
dismo::response(glm_model_1)

GLM Model 2 - expert variables with quadratics

In this model, we include quadratic terms for the covariates. This is a common approach in species distribution modelling to account for non-linear relationships between the predictors and the response variable. This increases the complexity of the model and allows for more flexibility in fitting the data.

glm_model_2 <- glm(Presence ~ 
                     BIO5_Max_Temp_Warmest_Month + I(BIO5_Max_Temp_Warmest_Month^2) + 
                     BIO6_Min_Temp_Coldest_Month + I(BIO6_Min_Temp_Coldest_Month^2) + 
                     BIO12_Annual_Precipitation + I(BIO12_Annual_Precipitation^2) + 
                     BIO15_Precip_Seasonality + I(BIO15_Precip_Seasonality^2), 
                   data=train_PB_covs_thinned,
                   family = binomial(link = "logit"))

# Check the model results
summary(glm_model_2)

Call:
glm(formula = Presence ~ BIO5_Max_Temp_Warmest_Month + I(BIO5_Max_Temp_Warmest_Month^2) + 
    BIO6_Min_Temp_Coldest_Month + I(BIO6_Min_Temp_Coldest_Month^2) + 
    BIO12_Annual_Precipitation + I(BIO12_Annual_Precipitation^2) + 
    BIO15_Precip_Seasonality + I(BIO15_Precip_Seasonality^2), 
    family = binomial(link = "logit"), data = train_PB_covs_thinned)

Coefficients:
                                   Estimate Std. Error z value Pr(>|z|)    
(Intercept)                      -8.261e+01  1.857e+01  -4.448 8.66e-06 ***
BIO5_Max_Temp_Warmest_Month      -1.284e+00  1.207e+00  -1.064   0.2874    
I(BIO5_Max_Temp_Warmest_Month^2)  1.218e-02  1.953e-02   0.623   0.5330    
BIO6_Min_Temp_Coldest_Month      -1.010e+00  1.917e-01  -5.268 1.38e-07 ***
I(BIO6_Min_Temp_Coldest_Month^2)  1.384e-01  1.286e-02  10.758  < 2e-16 ***
BIO12_Annual_Precipitation        1.053e-03  1.964e-03   0.536   0.5917    
I(BIO12_Annual_Precipitation^2)  -1.353e-06  7.008e-07  -1.931   0.0535 .  
BIO15_Precip_Seasonality          2.036e+00  2.384e-01   8.539  < 2e-16 ***
I(BIO15_Precip_Seasonality^2)    -8.983e-03  1.272e-03  -7.059 1.67e-12 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

(Dispersion parameter for binomial family taken to be 1)

    Null deviance: 8758.5  on 11463  degrees of freedom
Residual deviance: 5550.0  on 11455  degrees of freedom
AIC: 5568

Number of Fisher Scoring iterations: 6

# These response curves don't look very helpful
dismo::response(glm_model_2)

Model effect evaluation

Here we use a function presented in an EcoCommons Australia notebook to evaluate the model performance. The notebook can be found on their GitHub: https://github.com/EcoCommonsAustralia/notebooks/tree/main/notebooks.

# Function to plot effect size graph
plot_effect_size <- function(glm_model) {
  # Check if required libraries are installed
  if (!requireNamespace("ggplot2", quietly = TRUE)) {
    stop("Please install the 'ggplot2' package to use this function.")
  }
  library(ggplot2)

  # Extract effect sizes (coefficients) from the model
  coefs <- summary(glm_model)$coefficients
  effect_sizes <- data.frame(
    Variable = rownames(coefs)[-1],  # Exclude the intercept
    Effect_Size = coefs[-1, "Estimate"],
    Std_Error = coefs[-1, "Std. Error"]
  )

  # Sort by effect size
  effect_sizes <- effect_sizes[order(-abs(effect_sizes$Effect_Size)), ]

  # Plot the effect sizes with error bars
  ggplot(effect_sizes, aes(x = reorder(Variable, Effect_Size), y = Effect_Size)) +
    geom_bar(stat = "identity", fill = "#11aa96") +
    geom_errorbar(aes(ymin = Effect_Size - Std_Error, ymax = Effect_Size + Std_Error), width = 0.2) +
    coord_flip() +
    labs(
      title = "Effect Sizes of Variables",
      x = "Variable",
      y = "Effect Size (Coefficient Estimate)"
    ) +
    theme_minimal()
}

Use the function to check the effect sizes

We need to be careful when interpreting the effect sizes of models with quadratic terms however, as the response curve depends on the linear and the quadratic term.

# Example usage of effect size plot
plot_effect_size(glm_model_1)

plot_effect_size(glm_model_2)

Response curves

Again, we can use a function from the EcoCommons notebook to plot the response curves from the model, although for quadratics we need to adjust the function or use something else.

plot_species_response <- function(glm_model, predictors, data) {
  # Check if required libraries are installed
  if (!requireNamespace("ggplot2", quietly = TRUE) || !requireNamespace("gridExtra", quietly = TRUE)) {
    stop("Please install the 'ggplot2' and 'gridExtra' packages to use this function.")
  }
  library(ggplot2)
  library(gridExtra)

  # Create empty list to store response plots
  response_plots <- list()

  # Loop through each predictor variable
  for (predictor in predictors) {
    # Create new data frame to vary predictor while keeping others constant
    pred_range <- seq(
      min(data[[predictor]], na.rm = TRUE),
      max(data[[predictor]], na.rm = TRUE),
      length.out = 100
    )
    const_data <- data[1, , drop = FALSE]  # Use first row to keep other predictors constant
    response_data <- const_data[rep(1, 100), ]  # Duplicate the row
    response_data[[predictor]] <- pred_range

    # Predict probabilities
    predicted_response <- predict(glm_model, newdata = response_data, type = "response")

    # Create data frame for plotting
    plot_data <- data.frame(
      Predictor_Value = pred_range,
      Predicted_Probability = predicted_response
    )

    # Add presence and absence data
    presence_absence_data <- data.frame(
      Predictor_Value = data[[predictor]],
      Presence_Absence = data$Presence
    )

    # Generate the response plot
    p <- ggplot() +
      
      geom_line(data = plot_data, 
                aes(x = Predictor_Value, y = Predicted_Probability), 
                color = "#61c6fa", linewidth = 1) +
      
      geom_point(data = presence_absence_data[presence_absence_data$Presence_Absence == 1, ], 
                 aes(x = Predictor_Value, y = Presence_Absence), 
                 color = "#11aa96", alpha = 0.6) +
      
      geom_point(data = presence_absence_data[presence_absence_data$Presence_Absence == 0, ], 
                 aes(x = Predictor_Value, y = Presence_Absence), 
                 color = "#f6aa70", alpha = 0.6) +
      
      labs(x = predictor, y = NULL) +
      theme_minimal() +
      theme(axis.title.y = element_blank())

    # Store the plot in the list
    response_plots[[predictor]] <- p
  }

  # Arrange all plots in one combined plot with a single shared y-axis label
  grid.arrange(
    grobs = response_plots,
    ncol = 3,
    left = "Predicted Probability / Presence-Absence"
  )
}

Use the response curve function

predictors <- c("BIO5_Max_Temp_Warmest_Month", 
                "BIO6_Min_Temp_Coldest_Month", 
                "BIO12_Annual_Precipitation", 
                "BIO15_Precip_Seasonality")

plot_species_response(glm_model_1, predictors, train_PB_covs_thinned)

Attaching package: 'gridExtra'

The following object is masked from 'package:randomForest':

    combine

The following object is masked from 'package:dplyr':

    combine

Model 1 partial responses

# Plot the partial responses
partial_response(glm_model_1, predictors = train_PB_covs_thinned[,predictors], main='GLM')

# Plot inflated response curves:
inflated_response(glm_model_1, predictors = train_PB_covs_thinned[,predictors], method = "stat3", lwd = 3, main='GLM') 

Model 2 partial responses

# Plot the partial responses
partial_response(glm_model_2, predictors = train_PB_covs_thinned[,predictors], main='GLM')

# Plot inflated response curves:
inflated_response(glm_model_2, predictors = train_PB_covs_thinned[,predictors], method = "stat3", lwd = 3, main='GLM') 

GLM predictions to current environment

Model 1

# Predict the presence probability across the entire raster extent
predicted_raster_model_1 <- predicts::predict(covs_current_expert, glm_model_1, type = "response")

# Plot the species distribution raster
plot(
  predicted_raster_model_1,
  range = c(0, 1),  # Set min and max values for the color scale
  main = "Relative Probability of Occurrence of Koalas in SEQ - GLM 1"
)

Model 2

# Predict the presence probability across the entire raster extent
predicted_raster_model_2 <- predicts::predict(covs_current_expert, glm_model_2, type = "response")

# Plot the species distribution raster
plot(
  predicted_raster_model_2,
  range = c(0, 1),  # Set min and max values for the color scale
  main = "Relative Probability of Occurrence of Koalas in SEQ - GLM 2"
)

Random forest

# Make a folder to save outputs

dir.create("Outputs/RF_outputs", showWarnings = F)

Data preparation

Calculate the case weights (down/up-weighting)

Because we have a ‘class imbalance’ (uneven number of presences and background points), we are making their ‘weight’ in the model equal.

presNum <- as.numeric(table(train_PB_covs_thinned$Presence)["1"]) # number of presences
bgNum <- as.numeric(table(train_PB_covs_thinned$Presence)["0"]) # number of backgrounds
weight <- ifelse(train_PB_covs_thinned$Presence == 1, 1, presNum / bgNum) # down-weighting

Prepare for fitting the RF model(s)

# If wanting to fit a classification model
# Convert the response to factor for producing class relative likelihood
train_PB_covs_thinned$Presence_Factor <- as.factor(train_PB_covs_thinned$Presence)

# For down-sampling, the number of background (0s) in each bootstrap sample should the same as presences
# (1s). For this, we use sampsize argument to do this.
# We need to choose the SMALLER number out of the two classes
sample_size <- c("0" = bgNum, "1" = bgNum)
sample_size <- c(bgNum)

Random Forest Model - expert covariates

Classification or regression model?

# # Specify the model formula - classification
# model_formula <- as.formula(Presence_Factor ~ 
#                               BIO5_Max_Temp_Warmest_Month + 
#                               BIO6_Min_Temp_Coldest_Month + 
#                               BIO12_Annual_Precipitation + 
#                               BIO15_Precip_Seasonality)

# Specify the model formula - regression
model_formula <- as.formula(Presence ~ 
                              BIO5_Max_Temp_Warmest_Month + 
                              BIO6_Min_Temp_Coldest_Month + 
                              BIO12_Annual_Precipitation + 
                              BIO15_Precip_Seasonality)

Fit the random forest model

This will throw a warning as we only have two unique values (0s and 1s), but in our case that is fine, and you can ignore the warning.

rf_1 <- randomForest::randomForest(formula = model_formula,
                                   data = train_PB_covs_thinned,
                                   weights = weight,
                                   ntree = 1000,
                                   sampsize = sample_size,
                                   replace = T, 
                                   importance=TRUE)

Warning in randomForest.default(m, y, ...): The response has five or fewer
unique values.  Are you sure you want to do regression?

Check the model results

# Model summary
rf_1

Call:
 randomForest(formula = model_formula, data = train_PB_covs_thinned,      weights = weight, ntree = 1000, sampsize = sample_size, replace = T,      importance = TRUE) 
               Type of random forest: regression
                     Number of trees: 1000
No. of variables tried at each split: 1

          Mean of squared residuals: 0.08464043
                    % Var explained: 24.02

# Variable importance:
importance(rf_1)

                              %IncMSE IncNodePurity
BIO5_Max_Temp_Warmest_Month  91.42738      67.35590
BIO6_Min_Temp_Coldest_Month 112.16890     103.63237
BIO12_Annual_Precipitation   81.56532      85.42466
BIO15_Precip_Seasonality     75.60041      46.61974

# Plot variable importance
varImpPlot(rf_1, type = 1)

# Look at single trees:
head(getTree(rf_1,1,T))

Partial dependence plots

# Now, we plot response curves in the same way as we did for GLMs above:
partial_response(rf_1, predictors = train_PB_covs_thinned[,predictors], main='Random Forest')

# Plot inflated response curves:
inflated_response(rf_1, predictors = train_PB_covs_thinned[,predictors], method = "stat3", lwd = 3, main='Random Forest') 

Random Forest predictions

# Predict the presence probability across the entire raster extent
predicted_raster_RF_1 <- predicts::predict(covs_current_expert, rf_1, type = "response")

# Plot the species distribution raster
plot(
  predicted_raster_RF_1,
  range = c(0, 1),  # Set min and max values for the color scale
  main = "Relative Probability of Occurrence of Koalas in SEQ - RF 1"
)

Model evaluation with spatial block cross-validation

# Convert training data to sf
train_PB_covs_thinned_sf <- st_as_sf(train_PB_covs_thinned[, c("x", "y", "Presence")], coords = c("x", "y"), crs = "EPSG:3112")

# Generate spatial blocks
spblock <- cv_spatial(x = train_PB_covs_thinned_sf, 
                      column = "Presence",
                      r = NULL,
                      size = 50000, # Size of the blocks in metres
                      k = 5,
                      hexagon = TRUE,
                      selection = "random",
                      iteration = 100, # to find evenly-dispersed folds
                      biomod2 = FALSE)

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  train_0 train_1 test_0 test_1
1    1185    9043    279    957
2    1187    8317    277   1683
3    1176    9185    288    815
4    1177    8352    287   1648
5    1131    5103    333   4897

cv_plot(cv = spblock,
        x = train_PB_covs_thinned_sf,
        points_alpha = 0.5,
        nrow = 2)

# Extract the folds to save 
spfolds <- spblock$folds_list

# We now have a list of 5 folds, where the first object is the training data, and the second is the testing data
str(spfolds)

List of 5
 $ :List of 2
  ..$ : int [1:10228] 10859 10657 10911 10860 10753 10806 10912 10804 10805 11020 ...
  ..$ : int [1:1236] 10667 11031 10666 10816 10766 10767 10713 10714 10758 10716 ...
 $ :List of 2
  ..$ : int [1:9504] 10859 10657 10911 10860 10753 10806 10912 10804 10805 11020 ...
  ..$ : int [1:1960] 11263 11226 11225 11129 11128 11223 11264 11267 11022 11075 ...
 $ :List of 2
  ..$ : int [1:10361] 10859 10657 10911 10860 10753 10806 10912 10804 10805 11020 ...
  ..$ : int [1:1103] 6493 2803 2195 11249 5437 5068 11305 2966 11308 11385 ...
 $ :List of 2
  ..$ : int [1:9529] 10859 10657 10911 10860 10753 10806 10912 10804 10805 11020 ...
  ..$ : int [1:1935] 10530 10571 10619 10575 10327 10330 10574 10579 10532 3891 ...
 $ :List of 2
  ..$ : int [1:6234] 11263 11226 11225 11129 11128 11223 11264 11267 11022 11075 ...
  ..$ : int [1:5230] 10859 10657 10911 10860 10753 10806 10912 10804 10805 11020 ...

Run the model for every fold and evaluate

Model evaluation - metrics

Typically, it helps to evaluate your model with several metrics that describe different features of model performance and prediction. Here, we define a function to feed in a model prediction and calculate several evaluation metrics.

The metrics are:

-Area under the receiver operating characteristic curve (AUC ROC)

Higher values of this (closer to 1) suggest a model is good at distinguishing presence points from the background.

-Continuous boyce index

Higher values of this (closer to 1) suggest a model is good at predicting higher suitability at spots where there were presences.

# Start a dataframe to save results
eval_df <- data.frame(fold = numeric(),
                      ROC = numeric(),
                      boyce = numeric())

for(f in seq_along(spfolds)) {
  
  # Subset the training and testing data (spatial cross validation) (for the fth fold)
  
  train_PB_covs_scv <- train_PB_covs_thinned[spfolds[[f]][[1]], ]
  test_PB_covs_scv <- train_PB_covs_thinned[spfolds[[f]][[2]], ]
  
  glm_model_1 <- glm(Presence ~ 
                     BIO5_Max_Temp_Warmest_Month + 
                     BIO6_Min_Temp_Coldest_Month + 
                     BIO12_Annual_Precipitation + 
                     BIO15_Precip_Seasonality,
                   data=train_PB_covs_scv,
                   family = binomial(link = "logit"))
  
    # Predict to the testing data of fold f
  test_PB_covs_scv$pred <- predict(glm_model_1, newdata = test_PB_covs_scv, type = "response")

  # Evaluate prediction on test set
  ROC = precrec::auc(precrec::evalmod(scores = test_PB_covs_scv$pred, labels = test_PB_covs_scv$Presence))[1,4]
 
  boyce = ecospat::ecospat.boyce(fit = test_PB_covs_scv$pred, 
                                 obs = test_PB_covs_scv$pred[which(test_PB_covs_scv$Presence==1)], 
                                 nclass = 0, # Calculate continuous index
                                 method = "pearson",
                                 PEplot = F)[["cor"]]
  
  # Add results to dataframe
  eval_df <- eval_df %>% add_row(fold = f, ROC = ROC, boyce = boyce)

  
}

Summarise the evaluation metrics

# Mean AUC & boyce
eval_df %>% 
  summarise(mean_AUC = mean(ROC),
            mean_boyce = mean(boyce),
            sd_AUC = sd(ROC),
            sd_boyce = sd(boyce))

Model evaluation for Random Forest with spatial block cross-validation

We’re going to use the same spatial folds as before.

Run the RF model for every fold and evaluate

# Start a dataframe to save results
eval_df.RF <- data.frame(fold = numeric(),
                      ROC = numeric(),
                      boyce = numeric())

for(f in seq_along(spfolds)) {
  
  # Subset the training and testing data (spatial cross validation) (for the fth fold)
  
  train_PB_covs_scv <- train_PB_covs_thinned[spfolds[[f]][[1]], ]
  test_PB_covs_scv <- train_PB_covs_thinned[spfolds[[f]][[2]], ]
  
  presNum <- as.numeric(table(train_PB_covs_scv$Presence)["1"]) # number of presences
  bgNum <- as.numeric(table(train_PB_covs_scv$Presence)["0"]) # number of backgrounds
  weight <- ifelse(train_PB_covs_scv$Presence == 1, 1, presNum / bgNum) # down-weighting
  
  sample_size <- c("0" = bgNum, "1" = bgNum)
  sample_size <- c(bgNum)

  
  rf_1 <- randomForest::randomForest(formula = model_formula,
                                   data = train_PB_covs_scv,
                                   weights = weight,
                                   ntree = 1000,
                                   sampsize = sample_size,
                                   replace = T, 
                                   importance=TRUE)
  
  
    # Predict to the testing data of fold f
  test_PB_covs_scv$pred <- predict(rf_1, newdata = test_PB_covs_scv, type = "response")

  # Evaluate prediction on test set
  ROC = precrec::auc(precrec::evalmod(scores = test_PB_covs_scv$pred, labels = test_PB_covs_scv$Presence))[1,4]
 
  boyce = ecospat::ecospat.boyce(fit = test_PB_covs_scv$pred, 
                                 obs = test_PB_covs_scv$pred[which(test_PB_covs_scv$Presence==1)], 
                                 nclass = 0, # Calculate continuous index
                                 method = "pearson",
                                 PEplot = F)[["cor"]]
  
  # Add results to dataframe
  eval_df.RF <- eval_df.RF %>% add_row(fold = f, ROC = ROC, boyce = boyce)

  
}

Warning in randomForest.default(m, y, ...): The response has five or fewer
unique values.  Are you sure you want to do regression?
Warning in randomForest.default(m, y, ...): The response has five or fewer
unique values.  Are you sure you want to do regression?
Warning in randomForest.default(m, y, ...): The response has five or fewer
unique values.  Are you sure you want to do regression?
Warning in randomForest.default(m, y, ...): The response has five or fewer
unique values.  Are you sure you want to do regression?
Warning in randomForest.default(m, y, ...): The response has five or fewer
unique values.  Are you sure you want to do regression?

Summarise the evaluation metrics

# Mean AUC & boyce
eval_df.RF %>% 
  summarise(mean_AUC = mean(ROC),
            mean_boyce = mean(boyce),
            sd_AUC = sd(ROC),
            sd_boyce = sd(boyce))

Make predictions to future climates

Load future environmental data

covs_future <- rast("Data/Environmental_variables/future_bioclim.2090.SSP370.tif")
names(covs_future) <- layer_names
covs_future

class       : SpatRaster 
dimensions  : 47, 55, 19  (nrow, ncol, nlyr)
resolution  : 5123.954, 5123.954  (x, y)
extent      : 1621552, 1903370, -3349594, -3108768  (xmin, xmax, ymin, ymax)
coord. ref. : GDA94 / Geoscience Australia Lambert (EPSG:3112) 
source      : future_bioclim.2090.SSP370.tif 
names       : BIO1_~_Temp, BIO2_~Range, BIO3_~ality, BIO4_~ality, BIO5_~Month, BIO6_~Month, ... 
min values  :   0.8177757,   0.3121004,    1.564732,    12.43535,    1.130271,   0.4521889, ... 
max values  :  24.5521488,  14.5486765,   50.989292,   528.63293,   37.389927,  15.7586107, ... 

covs_future <- terra::mask(covs_future, covs_current) # Crop to SEQ extent

covs_future_expert <- subset(covs_future, names(covs_future) %in% c("BIO5_Max_Temp_Warmest_Month", 
                                                                    "BIO6_Min_Temp_Coldest_Month", 
                                                                    "BIO12_Annual_Precipitation", 
                                                                    "BIO15_Precip_Seasonality"))

Plot the future rasters

for(i in 1:nlyr(covs_future)) {
  terra::plot(covs_future[[i]], main = names(covs_future)[[i]])
}

# Plot to compare the difference between the current and future rasters

plot(covs_future_expert - covs_current_expert)

Test the environmental distance between current data and future conditions

mess <- predicts::mess(covs_future_expert, 
                       train_PB_covs_thinned[, c("BIO5_Max_Temp_Warmest_Month", 
                                            "BIO6_Min_Temp_Coldest_Month", 
                                            "BIO12_Annual_Precipitation", 
                                            "BIO15_Precip_Seasonality")])

plot(mess, axes = F)

r_mess_mask <- mess < 0
plot(r_mess_mask, axes=F)

Test which areas you might mask out because they are ‘novel’ in environmental space and therefore require model extrapolation.

analog_fut <- predicted_raster_model_1

values(analog_fut)[values(mess)<0] <- NA

plot(analog_fut, 
     range = c(0, 1),  # Set min and max values for the color scale
     main = "Koala relative occurrence in regions with analogue conditions")

novel_fut <- predicted_raster_model_1

values(novel_fut)[values(mess)>0] <- NA

plot(novel_fut, 
     range = c(0, 1),  # Set min and max values for the color scale
     main = "Koala relative occurrence in regions with novel conditions")

GLM future predictions

Model 1

# Predict the presence probability across the entire raster extent
predicted_raster_model_1 <- predict(covs_future_expert, glm_model_1, type = "response")

# Plot the species distribution raster
plot(
  predicted_raster_model_1,
  range = c(0, 1),  # Set min and max values for the color scale
  main = "Relative Probability of Occurrence of Koalas in SEQ - GLM1"
)

Model 2

# Predict the presence probability across the entire raster extent
predicted_raster_model_2 <- predict(covs_future_expert, glm_model_2, type = "response")

# Plot the species distribution raster
plot(
  predicted_raster_model_2,
  range = c(0, 1),  # Set min and max values for the color scale
  main = "Relative Probability of Occurrence of Koalas in SEQ - GLM2"
)

Random Forest future predictions

Model 1

# Predict the presence probability across the entire raster extent
predicted_raster_RF_1 <- predicts::predict(covs_future_expert, rf_1, type = "response", na.rm=TRUE)

# Plot the species distribution raster
plot(
  predicted_raster_RF_1,
  range = c(0, 1),  # Set min and max values for the color scale
  main = "Relative Probability of Occurrence of Koalas in SEQ - RF"
)

Presenting predictions with uncertainty

There are many sources of model uncertainty that should be explored and ideally, presented alongside model predictions.

One that we’ll focus on here is climate scenario uncertainty. We do so by fitting a second model to future climate data from a lower emission shared socioeconomic path scenario (SSP 1.26).

Load future environmental data (SSP 1.26)

covs_future_SSP126 <- rast("Data/Environmental_variables/future_bioclim.2090.SSP126.tif")
names(covs_future_SSP126) <- layer_names
covs_future_SSP126

class       : SpatRaster 
dimensions  : 47, 55, 19  (nrow, ncol, nlyr)
resolution  : 5123.954, 5123.954  (x, y)
extent      : 1621552, 1903370, -3349594, -3108768  (xmin, xmax, ymin, ymax)
coord. ref. : GDA94 / Geoscience Australia Lambert (EPSG:3112) 
source      : future_bioclim.2090.SSP126.tif 
names       : BIO1_~_Temp, BIO2_~Range, BIO3_~ality, BIO4_~ality, BIO5_~Month, BIO6_~Month, ... 
min values  :   0.7471204,   0.3128485,    1.585051,    12.19436,    1.046093,   0.3754203, ... 
max values  :  22.4384842,  14.8543510,   51.254021,   544.83429,   35.546104,  13.5217409, ... 

covs_future_SSP126_expert <- subset(covs_future_SSP126, names(covs_future_SSP126) %in% c("BIO5_Max_Temp_Warmest_Month", 
                                                                                          "BIO6_Min_Temp_Coldest_Month", 
                                                                                          "BIO12_Annual_Precipitation", 
                                                                                          "BIO15_Precip_Seasonality"))

Plot to compare the variables across the two scenarios

plot(covs_future_expert)

plot(covs_future_SSP126_expert)

GLM future predictions (SSP 1.26)

Model 1

# Predict the presence probability across the entire raster extent
predicted_raster_model_1_SSP126 <- predict(covs_future_SSP126_expert, glm_model_1, type = "response")

# Plot the species distribution raster
plot(
  predicted_raster_model_1,
  range = c(0,1),
  main = "SSP 3.70"
)

plot(
  predicted_raster_model_1_SSP126,
  range = c(0,1),
  main = "SSP 1.26"
)

Model uncertainty

Another element of uncertainty that can be represented is model uncertainty, or the standard error around the coefficient estimates.

# Extract standard errors of coefficients

coef_se <- summary(glm_model_1)$coefficients[, "Std. Error"]

print(coef_se)

                (Intercept) BIO5_Max_Temp_Warmest_Month 
               1.8309270981                0.0592126064 
BIO6_Min_Temp_Coldest_Month  BIO12_Annual_Precipitation 
               0.0360833444                0.0003325515 
   BIO15_Precip_Seasonality 
               0.0126551469 

covs_df <- as.data.frame(covs_future_expert, na.rm = FALSE)

pred_link <- predict(glm_model_1, newdata = covs_df, type = "link", se.fit = TRUE)

# Linear predictor (eta)
eta <- pred_link$fit
se_eta <- pred_link$se.fit

# Confidence intervals (95%)
z <- 1.96
eta_lower <- eta - z * se_eta
eta_upper <- eta + z * se_eta

# Transform back to response scale
linkinv <- glm_model_1$family$linkinv
predicted <- linkinv(eta)
lower_ci <- linkinv(eta_lower)
upper_ci <- linkinv(eta_upper)


# Add to covs_df
covs_df$predicted <- predicted
covs_df$lower_ci <- lower_ci
covs_df$upper_ci <- upper_ci


predicted_r <- setValues(rast(covs_future_expert, nlyr = 1), predicted)
lower_ci_r <- setValues(rast(covs_future_expert, nlyr = 1), lower_ci)
upper_ci_r <- setValues(rast(covs_future_expert, nlyr = 1), upper_ci)

# Step 2: Name the layers
names(predicted_r) <- "predicted"
names(lower_ci_r) <- "lower_CI"
names(upper_ci_r) <- "upper_CI"

prediction_w_uncertainty <- c(predicted_r, lower_ci_r, upper_ci_r)

plot(prediction_w_uncertainty, range = c(0, 1))